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Old 19th February 2008, 08:12 PM   #431
gl is offline gl  United States
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Hi Ian,

That's good news regarding the JFETs. I agree with William on the matching. I would go with matching Vgs at the Id you are planning to use. Beyond that it's a matter of trying different pairs in the circuit until you find a pair you like best. But that's a lot of trouble.

The ZTX550's aren't all that critical. I would say use anything with an hfe of 100 or more, Vce of 60V or more, and Pd of 600mW or more - although my preference on this last would be 1000mW.

The amps continue to perform really well. The one big improvement I note is their ability to unravel complex musical textures much better than before.

Cheers,
Graeme
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Old 23rd February 2008, 02:40 PM   #432
daly41k is offline daly41k  United States
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Default aleph 1.2 to xa100

GL, what is your listening expeirence been with your modified amps in the low bass region. I am using mine as treble/mid range amps where they sound excellent. I only used them for a short time full range on some Watkins WE-1's when testing. These speakers have three 8" woofers. One of the three acts as a subwoofer. These are acoustic suspension types and need a lot of current to set off the bass. The XA100 reminded me more of the Aleph's in pushing bass drivers. The 350.5 and my A75 were much better in the low bass region.

The reason I ask is that you use yours full range. thanks, dave
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Old 24th February 2008, 12:12 AM   #433
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I have bee reading up on the aricles and on Williams efforts .

I will try and graph the characteristics

Hope to have more to report soon

iMac
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Old 24th February 2008, 05:44 PM   #434
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I measured the the Ids of the j74 yesterday.

I got enough with close matching within 0.05 ma to consider 3 pairs in parrallel.

Will measure the Vgs tonight.

Graeme,

I was thinking about the resister to ground and why it influences the DC ? Any ideas.

iMac
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Old 25th February 2008, 05:15 PM   #435
gl is offline gl  United States
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Hi Dave,

My listening impressions to date are:

1) The musical lines are definitely cleaner. The micro-detail level has increased so that I can hear more of the low level stuff that's going on. The word "unravel" comes to mind regarding the musical textures.

2) It's as if the light level on the sound stage has been turned up a notch. There are fewer shadows. I don't believe that this has anything to do with tipping the tonal balance toward treble or bass or any of that old yin and yang stuff people talk about with the Alephs. This effect has improved my listening enjoyment a lot.

3) Bass is cleaner, more solid and more articulate. This improved still more going from 10K to 22K with the MacMillan resistors.

OK. Enough of the Stereophile style narrative. All of these effects are modest. So if I was you I wouldn't get obsessed about upgrading. I have kept my old MOSFET boards and I may switch back in a few months to see what I think. I have never heard an Aleph so I can't comment on the comparison of the bass performance.

At this point I've moved on to creating an active crossover for the MG3.6's. I've come up with two versions of a UGS type circuit to provide gain and balanced output. One of these is now in the system as a temporary line amp, for listening tests and tune up.

Cheers,
Graeme
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Old 25th February 2008, 05:25 PM   #436
gl is offline gl  United States
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Hi iMac,

Sounds like your J74's are plenty close enough. Three pairs sounds like a cool thing to try as well.

I haven't given the gate to ground resistors more thought. That would involve dusting off my old text books and doing some real work.

Graeme
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Old 27th February 2008, 12:53 AM   #437
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Quote:
At this point I've moved on to creating an active crossover for the MG3.6's. I've come up with two versions of a UGS type circuit to provide gain and balanced output. One of these is now in the system as a temporary line amp, for listening tests and tune up.
I would like to see the schematic--perhaps you will start a new thread?

JJ
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Old 27th February 2008, 04:19 PM   #438
gl is offline gl  United States
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I will start a new thread when I've gotten a bit farther along. On page 1 of the "UGS adventures" thread there is link to a preliminary schematic of one of the versions. It contains several mistakes. As you can see, this project dates back a long way and is a graphic demonstration of how long I take to get things done.

I have made different design decisions from some of those in the UGS Adventures thread.

The project is essentially a line amp and active crossover combined into one unit.

Graeme
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Old 27th February 2008, 10:15 PM   #439
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Quote:
The project is essentially a line amp and active crossover combined into one unit.
Nice!

I have been wondering if it is possible implement Rod Elliots "ELF " integrator into a BOSOZ or Pumpkin type circuit. Your circuit would probably answer some questions.

JJ

PS--sorry for the OT. This will surely need to be moved to the new thread at some point in the future.
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Old 2nd March 2008, 03:01 AM   #440
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Hi Graeme,

I just want to confirm your current setup in terms of McMillian resisters, the input to ground resisters and any other tweaks so i can compare notes. Can you also please confirn the zenor orientation.

On the input to ground resisters my understanding is 22K reduces the closed loop gain or increases the feeback. Perhaps this is why the offset is lower? I just wonder what the closed loop gain is compared to 10Kinput to ground resisters? 6db.

I have made a small daughter vero board for the dual matched quad 2SJ74's!

imac
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